/Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/Collision/ContactPoint.h
The order here is the order of preference in the solver. I.e., we like to solve Plane contacts before edge contacts before vertex contacts. This is most impotant for collisions against triangle meshes (or any concave shape) where the second shape is always the triangle, and so a PlaneVertex collision counts as a vertex collision.
namespace Chaos { enum EContactPointType { Unknown, VertexPlane, EdgeEdge, PlaneVertex, VertexVertex, } }